Electrostatic air filter

ABSTRACT

An air cleaner is provided comprising a filter assembly, an electrical power pack, and interconnecting high-voltage transmission means. The filter assembly is constructed of a filter unit having a prefilter and two layers of a dielectric filter media between which is sandwiched a positively charged grid. The filter assembly further includes a pair of negatively charged plates between which the filter unit is placed, and a header assembly molded of a rigid plastic and which is also provided with the male high-voltage receptacle and high-voltage contacts to the anode grid.

0 United States Patent [191 n n 3,763,633 Soltis [45] Oct. 9, 1973 [54]ELECTROSTATIC AIR FILTER 3,307,332 3/1967 Grace et a1. 55/131 [761Inventor Charles W Soms, -647 W- j 251323 iiiiiiiii; :12:: l HoustonTeX- 3,509,696 5/1970 Thompson 55/131 [22] Filed: Feb. 9, 1971 PrimaryExamner-Bemard Nozick [2u Appl' No" 113383 Attorney-Kane, Dalsimer,Kane, Sullivan & Kurucz [52] U.S. Cl...` 55/126, 55/131, 55/136, [57]ABSTRACT 55H39 55H46 5555//155254 5555/758255 55556158268 An air cleaneris provided comprising a filter assem- [51] Int Cl Bsc 3/41 bly, anelectrical power pack, and interconnecting [58] Fied 525 124high-voltage transmission means. The filter assembly is 55H26 139 146155 constructed of a filter unit having a prelter and two 485 486 524layers of a dielectric lter media between which is sandwiched apositively charged grid. The filter asseml bly further includes a pairof negatively charged plates [561 I References Cited between which thefilter unit is placed, and a header UN TED STATES PATENTS assemblymolded of a rigid plastic and which is also 2,822,058 2/1958 Roos et al55/131 provided with the male high-voltage receptacle and Kunz highvoltage contacts to the anode 3,073,094 l/l963 Landgraf et al. 55/13110/ 1963 Berly 55/138 15 Claims, 5 Drawing Figures PAENIEncI 91915 SHUI2 Uf 2 INVENTOR CHAI@ 55 W. 50 7/5 QQQQQQ- QQQQQ QW, ad

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RNEYS ELECTROSTATIC AIR FILTER BACKGROUND OF THE INVENTION In the fieldof residential as well as industrial airconditioning systems, theconsumer today can purchase an electrostatic air cleaner or a fiberglassair filter. Electrostatic air cleaners are currently manufactured andsupplied by the Carrier Corporation, Honeywell Corporation as well asothers. These units, how- BRIEF-SUMMARY OF THE INVENTION The principalobject of the present invention is an electrostatic air filter designedfor operation is residential and small commercial air-conditioningsystems which is adapted to replace standard one-inch fiberglass' airfilters. f v

Another object is to'provide a filter than removes 90 percent and moreof particles, one micron and larger,

, and, at the same time, is designedto fit into the same space as thestandard one-inch fiberglass filter while maintaining high efficiencywith a relatively low pressure drop.

A further'object is to provide an electrostatic air filter employing acombination of electrostatic and mechanical filtration and the desirablecharacteristics of both by employing a multilayer charged mediaarrangement which offers the following advantages:

l. The filter unit is only one-inch thick and can fit into thel samespace as existing air-conditioning filters;

2. no duct modifications are required for installation;

3. a disposable synthetic fiber collector isl employed which is veryeasily'serviced; and

4. the filter `is of significantly reduced cost. `A still further objectofthe filter of this invention is to provide effective relief throughfiltration in both residential and commercial buildings for allergysufferers.

A still further object is to provide an electrostatic air filter that isadapted to operate at substantial reduction of ozone emission incidentto ion generation as compared to the' commercially` available electronicair cleaners.

BRIEFDESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a perspective view of a representative airheating orconditioning unit in which the electrostatic air filter of the presentinvention is incorporated;

FIG. 2 is an exploded perspective yview. showing the components of thefilter;

FIG. 3 is a fragmentary perspective view of a collection filter sandwichhaving filter media in which a wire screen is embedded;

FIG. 4 is an enlarged longitudinal sectional view showing the completefilter assembly in which a conductive prefilter and two layers ofdielectric filter media are associated with positively and negativelycharged surfaces and a header assembly; and

FIG. 5 is a diagrammatic view of the components shown in FIG. 4illustrating the manner in which the desired electrostatic charge isgenerated for the desired ion flow within the filter assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENTS ln the drawings, anelectrostatic air cleaner 10 is shown operatively associated with anexemplary furnace l2 typical of the down-flow variety which, naturally,may be of the u p-flow or horizontal design or, for that matter, unit l2may be simply a residential, commercial or industrial air-conditioningsystem. Air cleaner l0, under any circumstances, will include a filterassembly 14, power pack 16 and interconnecting high-voltage power cable18.

The filter assembly 14 is adapted to remove large dust and lintparticles and very fine particles, one micron and larger. Specifically,this assembly' will remove up to percent or more of such particlesincludingv smog, dust, pollen, mold bacteria and other'contaminants aswell. Towards this end, the filter assembly 14 includes a filter unit I9which has a conductive prefilter 20 for removing large dust and lint.This partially conditioned air then passes through the high-voltageionizing field, causing the very fine particles to become charged andadhere to the filter media layers 22 and 24 of the collector pad or cell2l of sandwich construction in which the filter media 22 and 24 sandwichinterposed wire screen or grid 26 which is desirably made of fine wireto obtain optimum ion concentration. As will be evident to those skilledin the art, any one of the filter media 22 or 24 can be eliminated whilestill obtaining the desired ion flow. Both the prefilter 20 and filtermedia sandwich pad or cell 2l may have an individual or a common frame-28 whereby one may be removed or replaced but not the other. A housing30 may also be provided as part of the assembly 14 and may includeheader 32 and opposed front and rear screens 34 and 36, respectively.Naturally, front screen 34 may be shifted to a location betweenprefilter 20 and filter media 22 if desired whereupon prefilter 20 neednot be conductive. It is also contemplated that the opposed sides of thefilter cell 2l may have a conductive surface of coating applied theretoinstead of employing such screens. g t

In accordance with a successful embodiment of the present invention, theprefilter 20 of the filter assembly 14 embodied anominal k inch thickexpanded aluminum foil coated withany one of-a number of commerciallyavailable sticky coatings where desired or necessary for optimizing theefficiency of the prefilter. In addition, the successful embodimentincluded approximately V4 inch thick polyester fiber filter-media layers22 and 24 which sandwich interposed layer of 8 mesh commerciallyavailable screen wire serving -as grid 26. Obviously, any type ofdielectric material 22 and 24 may be employed and, towards this end,filter media layers 22 and 24 may assume the form of an open cellplastic foam material which has the added advantage of being washable asdistinct from being replaceable in the case of the polyester type offilter sandwich cell 2l.

As indicated, the front and rear screens 34 and 36` serve to hold thewashable or disposable prefilter 20 and filter cell 21 in position inthe air-conditioning unit. The front screen 34 is generally providedwith larger openings than the back screen 36 which serves to allow largelint particles to penetrate into the aluminum foil prefilter 20. Thesefront openings are approximately la inch squares in the statedsuccessful embodiment. This size is not critical to the high-efficiencyfilter performance. On the other hand, the rear screen forms the leavingair negative grid for the electrostatic filter and this screen iscomposed of V4 inch square openings. These openings could be smaller butit has been found that the optimum design is a balance between pressuredrop and percent opening. If the metal web of this screen 36 is too farapart, then the ions do not flow well into the positive grid 26 insidethe filter media layers 22 and 24.

In accordance with another successful embodiment of the invention, thefilter frame assembly included a perforated housing made from aluminumwhich was 64 percent open. The prefilter was formed from expandedaluminum and the filter media was open cell polyester and, specifically,flexible polyurethane foam. The anode grid was 8 mesh galvanized steelwire. The header assembly was rigid polyvinyl chloride and theanode/grid spacers are a rigid polyvinyl chloride.

It has been found that the effective life of the total disposable filter20 and filter cell 21 in the successful embodiment was approximately 2to 3 months when operated in a normal residential air-conditioning unit.The total efficiency was approximately 90 percent and more reduction ofone micron and larger particles which compares favorably with the moreexpensive electronic air cleaners that are commercially available. lnaddition, tests utilizing a Mast ozone meter indicated that the amountof ozone generated was negligible and no significant ozone build-upoccurred over a 24 hour period. Furthermore, there was significant andconvincing evidence of therapeutic benefit and advantage for allergysufferers. v

Referring now in more detail to the generation of the electrostaticfield, it will be initially noted that a wire pigtail" 38 iselectrically connected to the wire screen or grid 26 and, at the sametime, is adapted to be coupled with the high-voltage power lead 18 tothe positive side of the power pack 16. In accordance with the indicatedsuccessful embodiment, this pack 16 represented a 3,000 volt D.C. powersource at l milliamp. Optimum conditions of arcing, ozone and filterefficiency has been found to generally occur between 2,500 volts and3,500 volts. At this relatively low power level, the current is harmlesseven though the voltage is high. Power consumption is, accordingly, verylow and thereby maintaining at a minimum the cost of operation of thepack 16. The negative line is grounded to the air-conditioning unit forsafety. The front screen 34 and back screen 36 are connected to thecable 18 which may be two conductor co-axial power cable to the negativeside of the power pack 16. The negative side of the power pack 16 isgrounded, thus the entire system is ground with the exception of thepositive lead 38 to the grid 26. Inasmuch as the aluminum prefiltermaterial 20 is electrically conductive, it comes into intimate contactwith the front or airentering screen 34, is also grounded and takes on anegative charge. The two layers of polyester media 22 and 24 aredielectric and insulate the positive grid 26 from the negative front andrear screens 34 and 36, re-

spectively. When the disposable unit 19 is installed in the holdingframe constituted by header 32 and front and rear screens 34 and 36,respectively, and the wire lead 38 is coupled with the power pack 16through the cable 18, negative ions flow from the negative aluminum foilprefilter and the negative rear screen 36. The filter cell sandwich 21is so designed that the polyester media 22 and 24 in the successfulembodiment compresses slightly when installed to form a spacing of aboutthree-sixteenths inch between the positive grid 26 and the negativesurfaces. This spacing has been found to be fairly important if notcritical inasmuch as too close spacing will cause arcing and too largespacing will severely reduce the ion flow.

When the negative ions f'low from the negative to the positive grid,they hit or strike the dust particles causing them to precipitate on thepolyester media 22 and 24. The polyester media 22 and 24 forms a zig-zagpath for the particles forcing them to cross back and forth across thepath of the ions which are essentially flowing perpendicular to the gridsurfaces and parallel to the air flow. The polyester media 22 and 24,because of its dielectric characteristics, forms a capacitorlike designon the surfaces of the media and become highly charged opposite to thesurfaces next to the grid. The particles enter the negative field of thealuminum prefilter 20 and go through the first ion shower" in the firstlayer 22 of the polyester media and begin to precipitate out on to thismedia. Those particles that do not stick enter the second ion shower inthe second layer 24 of media and precipitate out on this media. Aninteresting characteristic of this embodiment is that the filter cell 2lbecomes more efficient as the media 22 and 24 become dirty, presumablybecause the small particles cling to the fibers and enlarge the exposedsurface for collecting the particles. This characteristic would appearto be opposite from a conventional electronic air cleaner which becomesless efficient as it gets dirty.

Thus, the several aforenoted objects and advantages are most effectivelyattained. Most important of all, the electrostatic air filter of thepresent invention offers the following advantages:

l. Compactness in that a high efficiency air filter is provided with athickness of less than l inch.

2. Filter media and conductive grid design and disposition provide forhighly efficient and effective ion flow.

3. Disposable filter unit is possible as a result of the selection ofmaterials that are relatively inexpensive.

4. Easy installation is provided in that the disposable filter unit maysimply replace the lower efficiency commonly employed one-inchfiberglass filter.

5. Low pressure drop is experienced because the combination of filtermaterials and electronics permit maximum filtration within the pressurelimits of the conventional residential air-conditioning system.

6. Filter unit configuration may assume different forms including thatillustrated in drawings herein or may be in the form of a roll which maybe turned to expose a new section thereof from time to time; or morethan one filter unit or cell or perhaps more individual layersthemselves may be employed to increase filter life and efficiency at aslightly higher pressure drop. In other words, modulation of filtermedia or cells are contemplated to obtain a multi-layer filterconstruction to satisfy certain commercial applications requiringfilters 2 inches or 3 inches thick. ln addition, the filter media, insuch instances, maybe foam of open cell construction with different poresizes for adjusting or obtaining different pressure drop across thethickness of the filter.

Although several preferred embodiments of the invention have beendisclosed and described in detail herein, it should be understood thatthis invention is in no sense limited thereby and its scope is to bedetermined by thel appended claims.

l claim:

ll. An electrostatic air filter comprising in combination: a filter unithaving a first relatively thin layer of dielectric filter media, asecond relatively thin layer of dielectric filter media disposed inclose proximity to the first layer, electrode means including a finewire grid interposed between and in close proximity with the first andsecond filter media, a pair of spaced conductive and chargeable surfaceson opposed sides of the dielectric layers away from the grid, a powerpack for supply ing a relatively high voltage at relatively low amperageto the filter unit, electrically conductive means for coupling the powerpack to the filter unit, the positive side of said power pack beingconnected to said fine wire grid and the negative side of said powerpack being connected to said chargeable surfaces whereby an imposedelectrostatic high-voltage ionizing field across the filter causes ionsto flow through the filter media and bombard very fine air-borneparticles and simultaneously cause their precipitation out onto themedia, and means for securing as an assembly the layers, interposed gridand chargeable surfaces.

2. The invention in accordance with claim l wherein the filter media isselected from the group consisting of polyester fibers and an open cellplastic foam filter material.

3. An electrostatic air filter comprising in combination: a filter unithavinglat least one relatively thin layer of dielectric filter media,conductive means including a fine wire grid in close proximity with thefirst filter media, a spaced conductive and chargeable surface on theoppositevside of one of the filter media away from the grid, a powerpack for supplying arelatively high voltage at relativelyvlow amperageto the filter unit, electrically conductive means forv coupling thepower lpack to the filter unit, the positive side of said power packbeing connected to said fine wire grid and the negative side of saidpower pack being connected to said chargeable surface for cooperating inimposing an electrostatic high voltage ionizing field acrossthe filtercausing ions to flow through the filter media and bombard very fineair-borne particles and simultaneously cause their precipitationv outonto the media, a prefilter means disposed in close proximity to one ofthe filter media and at the inlet side of the filter unit for filteringair passing through the pre-filter and removing air-borne large dustparticles and lint, and means for securing as an assembly the layer,chargeable surface,

grid and pre-filter.

4. The invention in accordance with claim 3 wherein a second relativelythin layer of dielectric filter media is disposed in close proximity tothe first layer and the conductive means is interposed and in closeproximity with the first and second filter media.

5. The invention in accordance with claim 4l wherein the pre-filter isconductive.

6. The invention in accordance with claim 4l wherein the prefilter isformed of' expanded aluminum foil.

7. The invention in accordance with claim 4 wherein the prefilter andfilter unit are positioned relative to one another by means of aperipherally extending frame.

8. The invention in accordance with claim 4 wherein the prefilter isaluminum foil approximately one-half inch thick and each of the filtermedia is ofv polyester fiber and is one-fourth inch thick and the gridis formed from a single layer of 8 mesh screen wire.

9. The invention in accordance with claim 4 wherein the electrostaticfilter unit is adapted to remove at least percent of the particles lmicron and larger from the 4 airstream.

l0. The' invention in accordance with claim 4 wherein a pair ofelectrically conductive perforated plates are spaced from one anotherand have interposed therebetween the prefilter and filter unit.

ill. The invention in accordance` with claim l0 wherein a non-conductiveheader is disposed about the periphery of the prefilter and filter unitand between the conductive perforated plates to dispose and position theprefilter and filter unit in a predetermined relationship between theperforated plates.

` l2. The invention in accordance with claim lll wherein means areprovided for electrically coupling the spaced screens and grid to arelatively high-voltage low-amperage power source and imposing upon theplates a'negative charge and the grid a positive charge whereupon ionsare adapted'to flow from the front plate through the electricallyconductive prefilter through one layer of dielectric filter media to thepositive grid and ions adapted to flow from the rear plate to theadjacent dielectric filter material to the positive grid, the ionsadapted to bombard the air-borne particles of the airstream beingfiltered causing the particles to precipitate out on to the filtermedia.

i3. The invention in accordance with claim l2 wherein the power sourceis adapted to supply voltag between 2,500 volts and 3,500 volts. V

14. The invention in accordance with claim i3 wherein the power sourcesupplies 3,000 volts D. C.

l5. The invention in accordance with claim l0 wherein the front screenhas larger openings than the back screen and the openings of the frontscreen are approximately inch squares and the openings in the rearscreen are approximately V4 inch squares.

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1. An electrostatic air filter comprising in combination: a filter unithaving a first relatively thin layer of dielectric filter media, asecond relatively thin layer of dielectric filter media disposed inclose proximity to the first layer, electrode means including a finewire grid interposed between and in close proximity with the first andsecond filter media, a pair of spaced conductive and chargeable surfaceson opposed sides of the dielectric layers away from the grid, a powerpack for supplying a relatively high voltage at relatively low amperageto the filter unit, electrically conductive means for coupling the powerpack to the filter unit, the positive side of said power pack beingconnected to said fine wire grid and the negative side of said powerpack being connected to said chargeable surfaces whereby an imposedelectrostatic high-voltage ionizing field across the filter causes ionsto flow through the filter media and bombard very fine air-borneparticles and simultaneously cause their precipitation out onto themedia, and means for securing as an assembly the layers, interposed gridand chargeable surfaces.
 2. The invention in accordance with claim 1wherein the filter media is selected from the group consisting ofpolyester fibers and an open cell plastic foam filter material.
 3. Anelectrostatic air filter comprising in combination: a filter unit havingat least one relatively thin layer of dielectric filter media,conductive means including a fine wire grid in close proximity with thefirst filter media, a spaced conductive and chargeable surface on theopposite side of one of the filter media away from the grid, a powerpack for supplying a relatively high voltage at relatively low amperageto the filter unit, electrically conductive means for coupling the powerpack to the filter unit, the positive side of said power pack beingconnected to said fine wire grid and the negative side of said powerpack being connected to said chargeable surface for cooperating inimposing an electrostatic high voltage ionizing field across the filtercausing ions to flow through the filter media and bombard very fineair-borne particles and simultaneously cause their precipitation outonto the media, a pre-filter means disposed in close proximity to one ofthe filter media and at the inlet side of the filter unit for filteringair passing through the pre-filter and removing air-borne large dustparticles and lint, and means for securing as an assembly the layer,chargeable surface, grid and pre-filter.
 4. The invention in accordancewith claim 3 wherein a second relatively thin layer of dielectric filtermedia is disposed in close proximity to the first layer and theconductive means is interposed and in close proximity with the first andsecond filter media.
 5. The invention in accordance with claim 4 whereinthe pre-filter is conductive.
 6. The invention in accordance with claim4 wherein the prefilter is formed of expanded aluminum foil.
 7. Theinvention in accordance with claim 4 wherein the prefilter and filterunit are positioned relative to one another by means of a peripherallyextending frame.
 8. The invention in accordance with claim 4 wherein theprefilter is aluminum foil approximately one-half inch thick and each ofthe filter media is of polyester fiber and is one-fourth inch thick andthe grid is formed from a single layer of 8 mesh screen wire.
 9. Theinvention in accordance with claim 4 wherein the electrostatic filterunit is adapted to remove at least 90 percent of the particles 1 micronand larger from the airstream.
 10. The invention in accordance withclaim 4 wherein a pair of electrically conductive perforated plates arespaced from one another and have interposed therebetween the prefilterand filter unit.
 11. The invention in accordance with claim 10 wherein anon-conductive header is disposed about the periphery of the prefilterand filter unit and between the conductive perforated plates to disposeand position the prefilter and filter unit in a predeterminedrelationship between the perforated plates.
 12. The invention inaccordance with claim 11 wherein means are provided for electricallycoupling the spaced screens and grid to a relatively high-voltagelow-amperage power source and imposing upon the plates a negative chargeand the grid a positive charge whereupon ions are adapted to flow fromthe front plate through the electrically conductive prefilter throughone layer of dielectric filter media to the positive grid and ionsadapted to flow from the rear plate to the adjacent dielectric filtermaterial to the positive grid, the ions adapted to bombard the air-borneparticles of the airstream being filtered causing the particles toprecipitate out on to the filter media.
 13. The invention in accordancewith claim 12 wherein the power source is adapted to supply voltagebetween 2,500 volts and 3,500 volts.
 14. The invention in accordancewith claim 13 wherein the power source supplies 3,000 volts D. C. 15.The invention in accordance with claim 10 wherein the front screen haslarger openings than the back screen and the openings of the frontscreen are approximately 3/4 inch squares and the openings in the rearscreen are approximately 1/4 inch squares.